Process of producing phthalic anhydride



Patented Oct. 30, 1928.

UNITED STATES, PATENT mm.

FRANK A. CANON AND GHESTEH E. ANDREWS, OI PITTSBURGH, PENNSYLVANIA, AS-SIGNORS TO THE SELDEN COIIANY, OF PITTSBURGH, PENNSYLVANIA, A 00R-PORATION OI DELAWARE.

PROCESS OT PRODUCING PHTHALIC ANHYDBIDE.

No Drawing. Original application nled June 20, 1882, Serial Ill'o.589.735 Divided and this application filed November '7, 1985. Serial No.87,885.

In the art of exothermic chemical reactions very practical .difiicultieshave been experienced in dissipating the excessive heat therebygenerated. p

In the air oxidation of naphthalene to hthalic anhydride the optimumtemperature is above 400 C., lying roughly between 400 C. and 450 0.,but much higher temperatures will also be reachedunless prevented.

It is the object of the present invention to provide an improved processfor carrying out exothermic chemical reactions of this character whichwill permit the zone of reaction to reach and maintain a desiredoperating is temperature, but will prevent its rise to an abnormal de ethereabove, the process beingr substantlally automatic in operation.

he present application is a'division of application, Serial No. 569,735,filed by us on June 20, 1922.

In processes of the above character in which the lower operatingtemperatures obtain, water has been employed as a cooling agent, and insomeres cts has ideal characteristics.

26 It is easily obtained, has reat thermal capacity and can beconvenienfiy directed and controlled. If properly brought intoheattransferring relationship to the catalyst and the reacting vapors,it will be caused to boil. This 30- will result in the absorption ofgreat quantities of heat from the catalyst. and the reacting gasesbecause of the large amount of heat latent heat of vaporization)required to efect its boiling operation.

as The use of mercury has been proposed but this material presentsserious difiiculties. In

. the first place its boiling int is too low for successful applicationwit out special thou h well-known methods of'treatment which (1 I 40materially to the cost of operation. Its high cost makes unlimited use,like that of water prohibitive. In addition it has a. relatively lowheat capacity and a relatively low rate of heat conductivity. (5oxidation and its hi h cessitates s ecial an cost y means for supportingan containing it.

In carrying out the present invention we have discovered that if acomposite metal,

consisting of one or more-metals that will boil below the desiredtemperature of the reactionand one or more metals that will boil It isalso subject to ific gravity neabove the said desired temperature of thereaction, is formed. in proper proportions, and this composite metal isplaced in heattransferring relation to the catalyst and the reactinggases, it will be caused to boil at a temperature close to butslightly'below the desired temperature of the reaction and may be thus made tocontrol the temperature of the reaction and kee the same well withinmaximum limits whi e permitting it to reach and maintain an eflicientminimum. In adf dition this composite metal will have a low meltingpoint, great thermal capacity and conductivity and relatively lowspecific gravity.

Taking the air oxidation process of converting naphthalene to phthalicanhydride as an example of the practlcal application of the invention, aheated mixture of air or other oxygen containing gas and naphthalene inthe vapor phase and at a suitable temperature is brought into thepresence of a suitable catalyst, for instance, vanadium oxide. 7 Thenaphthalene is thereby converted into phthalic anhydride and a lar eamount of heat is thereby generated, resu tin in high temperaturesunless controlled. perature as above. stated should run between 400 and450 C. and the desired temperature for the most effective working ofthis.

conversion process is ordinarily at approximately 425 C. Obviouslytemperatures materially above the same are not only undesirable butexperience has demonstrated that ver high temperature is detrimental tothe product and apt to be disastrous-to the reaction apparatus.

If cadmium which boils at 778 C. and mercury which has aboiling point at357 C.

be mixed in certain proportions a composition can be obtained having aboiling point which is close to that of .the desired reactiontemperature. Thus a composition made up oi 12% by weight, of cadmium and88% by he reaction temweight of mercury, is semi-liquid at 20 0..

and has a boiling int of approximately 370 0., whereas 40% y weight ofcadmium c ombined with 60% --by weight, of mercury, is liquid at about151 C. and boils at approximatelyv 430 C. If a working reactiontemperature of approximately 425 C. is taken as satisfactory, a boilingtemperature of about 400 C. for the controlling composition issubstantially satisfactor and this can be ob tained by a mixture 0 25%,by weight of cadmium and 75% by weight of mercury. is particular mixtureis liquid at about 100 C. and boils at approximatel 400 C. Thecomposition has other valua le features besides that of its boilingpoint. While the thermal conductivity of mercury is relatively low(.0189) that of cadmium is .215, so that the thermal conductivity of thecomposition is high, which is an important factor that assists it in itsheat-dissipating qualities. Moreover the specific gravity of thecomposition is less than that of mercury, the latter being 13.5 whilecadmium is 8.6.

In practicing the process the composite metal is brought into heattransferring relaof the herein described invention will be apparent tothose skilled in the art, without further description, and it will beunderstood that various changes .in the size, shape,

proportion and minor details of construction I may be resorted towithout departing from the spirit or sacrificing any of the advantagesof the invention.

What we claim, is: 1. The process of converting naphthalene to phthalicanhydride, which consists in subjecting' a mixture of naphthalene vaporand an oxygen-containing gas to a catalyst at a temperature rangingapproximately between 400 C.-450 0., and maintaining said temperature bytransmitting the excess heat generated to a com osition of cadmium andmercury that will Emil at said temperature and causin the composition tobe boiled by said excess eat.

2. The process of converting naphthalene to phthalic anhydride, whichconsists in subjecting a mixture of naphthalene vapor and anoxygencontaining gas to a catalyst at a mean temperature ofapproximately 425 C. and maintaining approximately said temperature bytransmitting the excess heat generated to a comggsition of cadmium andmercury that will G. and causing said excess composition.

3. The process of converting naphthalene to phthalic anhydride, whichconsists in subjecting naphthalene vapor and an oxygencontainin gas toacatalyst and preventing excessive heating by maintaining'a compositionofsubstantially 75% of mercury and 25% of cadmium in heat-transferringrelation therewith and causing said composition to be boiled by theexcess heat.

4. The air oxidation process of converting naphthalene to phthalicanhydride, which consists in causing a mixture of naphthalene vapor andair to react in the presence of a catalyst of vanadium oxide,maintaining a reaction temperature range between approximately 400excessive temperature of the catalyst and vapors by causing the excessheat of the reaction to boil a composition of approximately 75% mercuryand 25% cadmium.

' 5. A process ofconverting naphthalene to phthalic anhydride, whichconsists in subjecting naphthalene vapor and an oxygencontainin gas to acatalyst and preventing il at ap roximately 400 eat to boil saidexcessive eating by maintaininga composi- C. and 450 0., and preventingan tion of mercury and cadmium boiling at ap-' proximately the desiredreaction temperature in heat transferringrelation to the catalyst andcausing said composition to be boiled by the excess heat of thereaction.

In testimony whereof, we afiix our signatures.

FRANK AJcA'NoN. CHESTER E. ANDREWS.

